Considerations on harmonic impedance estimation in low voltage networks

One difficulty in calculating harmonic voltages and currents throughout a transmission or distribution system is the need for a precise model of the linear load, both in magnitude and composition, fed from each bus. It has become evident that the use of equivalents without a comprehensive check on the effects of all impedances actually present can lead to inaccurate estimation of the harmonic voltages and currents. Considerations on harmonic impedance estimation in low voltage networks are presented in the paper. Influences of model abstractions and uncertainties in parameter estimations are analyzed analytically and tested on a model of a real low voltage network. The parameters analyzed include different load compositions, cable lengths, lumping loads and feeders, and medium voltage network representations. It is observed that some of these parameter changes have only a minor effect on the frequency of the first parallel resonance, while other effects have to be included in the calculation to avoid misleading results. This analysis can be used as a guideline when harmonic voltages are estimated in low voltage networks.